Kepler-1625b and Kepler-1708b are Unlikely to Be Orbited by Large Exomoons, Astronomers Say

Astronomers Make New Discoveries in the Search for Exomoons

The vastness of our Solar System holds over 200 moons, but the challenge lies in detecting exomoons beyond our system due to their small sizes. Recent research, however, has shed light on two potential exomoons that orbit massive exoplanets, Kepler-1625b and Kepler-1708b, although their existence is still a subject of debate. In a groundbreaking study, astronomers have reanalyzed the data from the Hubble and Kepler telescopes to further investigate these exomoon candidates.

An artist’s impression of the gas giant Kepler 1625b with its large moon, Kepler 1625b-i; the pair has a similar mass and radius ratio to the Earth-Moon system but scaled up by a factor of 11. Image credit: Sci.News.

An artist’s impression of the gas giant Kepler 1625b with its large moon, Kepler 1625b-i; the pair has a similar mass and radius ratio to the Earth-Moon system but scaled up by a factor of 11. Image credit: Sci.News.

Since Galileo Galilei’s discovery of Jupiter’s four principal moons in 1610, moons have played a crucial role in advancing our understanding of planetary science. From evidence of cryovolcanism on Saturn’s moon Enceladus to the Copernican revolution triggered by Galileo’s findings, moons continue to provide fascinating insights. The anticipation of detecting moons around exoplanets has captivated astronomers for over a decade.

Thus far, two potential exomoon detections have been proposed, both originating from data collected by NASA’s Kepler space mission. The first candidate implies the presence of a Neptune-sized moon in a wide orbit around Kepler-1625b, a Jupiter-sized planet revolving around the evolved solar-type star Kepler-1625. More recently, the same team announced the second exomoon claim, suggesting a moon orbiting Kepler-1708b, another Jupiter-sized planet orbiting the solar-type main-sequence star Kepler-1708.

“Exomoons are located at such great distances that direct observation is currently beyond the capabilities of even the most advanced telescopes,” explained Dr. René Heller, an astrophysicist at the Max Planck Institute for Solar System Research. “Instead, telescopes record fluctuations in the brightness of distant stars, known as light curves.”

Astronomers analyze these light curves for any indications of moon presence. When an exoplanet passes in front of its star as seen from Earth, it causes a slight dimming of the star. This event, known as a transit, occurs regularly according to the orbital period of the planet. If an exomoon accompanies the planet, it would also cause a similar dimming effect. However, the exomoon’s impact on the light curve is much weaker and follows a complex pattern due to the moon and planet’s mutual gravitational interaction.

Detecting exomoons requires a meticulous approach. Dr. Heller and his colleague, Dr. Michael Hippke from Sonneberg Observatory, employed their open-source algorithm Pandora to calculate millions of simulated light curves for various exoplanet-moon sizes, distances, and orbital orientations. By comparing these simulated light curves with the observed data, they aimed to find the best match.

Their findings regarding Kepler-1708b indicate that scenarios without a moon are equally plausible, casting doubt on the presence of an exomoon. Dr. Hippke stated, “The probability of a moon orbiting Kepler-1708b is clearly lower than previously reported. The data do not suggest the existence of an exomoon around Kepler-1708b.” Similar doubts surround Kepler-1625b, as previous observations with the Kepler and Hubble telescopes failed to provide conclusive evidence.

The researchers highlight the significance of stellar limb darkening, a phenomenon where the brightness of a star appears darker towards its edges. The limb darkening effect observed in Kepler-1625b’s star differs depending on whether it is observed through the Kepler or Hubble telescope. Accounting for this effect in their modeling provides a more conclusive explanation for the data, suggesting that a giant exomoon may not exist.

This groundbreaking study, published in the journal Nature Astronomy, represents a significant step forward in the ongoing quest to detect exomoons. While the existence of these particular exomoons remains uncertain, the advancement of technology and the dedication of astronomers continue to push the boundaries of our knowledge about the vast universe beyond.

Additional Note:

Exomoons captivate astronomers due to their potential to reveal further insights into planetary science. These elusive celestial bodies, although challenging to detect, have the potential to unlock mysteries about the formation and evolution of exoplanetary systems. As scientists refine their techniques and technology, future discoveries may unveil the existence of exomoons, opening new avenues of exploration and deepening our understanding of the cosmos.

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